Almost 3 months later.... The only part of Sleeping Dogs that is online is their leaderboards. People on your friends list who also played the game would have their scores show up in your game. For example, if you were racing around the city and were traveling at a high speed for an extended period of time, it would pop up on the right with the message that you were making progress towards one of the in game challenges. It would also show you your friend's time who was next above your score and let you know when you passed it, and who the next person above them was as well. I don't know if that is still working though.

There WAS Triad Wars which was an online game, but not in an MMO sense. It is no longer around.